The present invention relates to an improved oxygen scavenging system which can be employed in multi-layer films, sheets, and molded or thermoformed shapes that find utility in low oxygen packaging for pharmaceuticals, cosmetics, oxygen sensitive chemicals, electronic devices, and in particular food packaging.
Organic oxygen scavenging materials have been developed partly in response to the food industry's goal of having longer shelf-life for packaged food.
One method which is currently being employed involves the use of "active packaging" where the package is modified in some way so as to control the exposure of the product to oxygen. Such "active packaging" can include sachets containing iron based compositions such as AGELESS.TM. which scavenges oxygen within the package through an oxidation reaction. However, such an arrangement is not advantageous for a variety of reasons including the accidental ingestion of the sachets or the oxygen-scavenging material present therein.
Other techniques involve incorporating an oxygen scavenger into the package structure itself. In such an arrangement, oxygen scavenging materials constitute at least a portion of the package, and these materials remove oxygen from the enclosed package volume which surrounds the product or which may leak into the package, thereby, in the case of food products, inhibiting spoilage and prolonging freshness.
Oxygen scavenging materials in this environment include low molecular-weight oligomers that are typically incorporated into polymers or can be oxidizable organic polymers in which either the backbone or, initially at least, side-chains of the polymer react with oxygen.
Such oxygen scavenging materials are typically employed with a suitable catalyst, e.g., an organic or inorganic salt of a transition metal catalyst such as cobalt. Examples of other suitable catalysts are organic and inorganic salts of iron, manganese, copper, and molybdenum. These materials are incorporated into one of the layers of the multi-layer films which are used in forming packaging materials.
While multi-layer films employing an oxygen scavenging material can be effective in the scavenging of oxygen, they can have certain disadvantages particularly in their preparation. For example, processability of a layer containing the oxidizable polymer and the catalyst can often be difficult.
That is, melt processing of this combination of components can be difficult, if not impossible, to accomplish without undesirable oxidation of the oxidizable polymer at the elevated temperature of the melt. Because of such premature oxidation during processing, the oxidizable resins which can be processed are somewhat limited.
One approach to solving this problem is to increase the concentration of stabilizers in the composition. High concentrations of stabilizers, however, tend to inhibit the desired oxygen scavenging reaction and also add to the overall cost of the film-forming composition.
Such problems can be particularly troublesome where the package is to be exposed to low temperatures, e.g., as for refrigerated or frozen foods. The scavenger needs to be both effective at low temperatures during the storage of packaged food, yet be capable of surviving melt processing at high temperatures. Unfortunately, it is difficult for a resin to meet such a combination of performance requirements.
Thus, the need still exists for an improved oxygen-scavenging system, particularly a system employed within multi-layer packaging films.